Method and apparatus for controlling radio receivers



K. W. JARVIS Mays, 1938.

METHOD AND APPARATUS. FOR CONTROLLING RADIO RECEIVERS Original Filed Feb. 13, 1952 4 Sheets-Sheet l m... HLN

K. w. JARvls 2,115,813

METHOD AND APPARATUS FOR CONTROLLING RADIO RECEIVERS May 3; 1938.

original Filed Feb. 15', 1952 4 sheets-shea te ATTORNEYS May 3, 1938- K. w. JARvls 2,115,813

METHOD AND APPARATUS Foa CONTROLLING RADIO RECEIVERS f original Filed Feb. 13, 1952 4 sheets-sheet 5 l l A il "o "5 1, |25 OUTPUT INPUT J :i

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METHOD AND APPARATUS FOR CONTROLLING RADIO RECEIVERS Original Filed Feb. 13, 1932 4 Sheets-Sheet 4 ummm...

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I ATTORNEYS Patented May 3, 1938 UNITED STATES PATENT OFFICE Kenneth W. Jarvis, Winnetka, Ill., assignor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application February 13, 1932, Serial No. 592,764

Renewed January 21, 1938 31 Claims.

This invention is concerned with radio or allied arts and particularly wherever it is desired to choose at will and more exactly any one of a number of energy carriers. Still more specifically it x deals with a new method of control in` such choosing, Vmeans for accomplishing the said control, and means for applying said contro-l units tothe various elements of the system to obtain the desired characteristics.

An object is the adding of supplementary control mechanisms of independent selective character to the ordinary selective networks.

Another object is the provision of independent control means sensitive to the frequency of the incoming signal acting at a point in the receiver as regards signal transmission subsequent to the point of actuation of the control means.

A further object is the .provision of additional methods of control in which the change in the operation of the receiver is made relatively abrupt at a predetermined small change of resonance frequency on either side of the point of exact tuning for the desired energy carrier, these points being so close to this point that reception is possible with a given energy carrier only in a narrow range of tuning on either side of the exact point of tuning for the energy carrier.y i

Another object is the use of means whereby the frequency response characteristics of a receiver when tuned to the energy carrier, are substantially those of the normal frequency selecting .circuits, but as the point of tuning of .the receiver is shifted from the resonance position for the carrier the change in response is much greater than that which the characteristics of the normal frequency selecting circuits would of themselves accomplish.

Another object is a provision of methods and of means whereby the receiver cannot be detuned very far from the carrier without the audio response falling below audibility.

Another object is the provision of methods and means whereby there is a large amount of no response tuning space between adjacent signals with the consequent removal of the possibility of reception of two stations, static noises, et cetera.

It has been the practice hitherto to achieve selection o-f a given energy carrier by the use of resonant or selective circuits. If a signal is impressed on such a resonant circuit at the natural frequency of the resonant circuit, the response within the circuit will be a maximum, falling away on either side as the resonance frequency of the receiver is tuned away from the frequency of the signal.

By proper provision of resonant-circuits we can within reason make this response as sharp as we like. It is to be remembered,l however, that the modulated energy carriers which constitute the incoming signal can be analyzed into the carrier A5 frequency, plus a bandof frequencies differingV from the carrier frequency plus and minus lby the highest modulation frequency which` is being transmitted. In order to secure faithful reproduction of the band frequencies in the proportion ..10 in which they exist in the incoming signal the selective characteristics of the circuit must be made relatively broad. On the other hand, if this is done the circuit fails in selectivity to the extent that signals on adjacent carrier frequencies l5 to the one desired are received to a greater or less extent. It is accordingly desirable to use a selective circuit which is sharper than is desirable for the greatest faithfulness of reproduction of the modulatedV frequencies and to compensate for ..20 the impaired reception of the side band frequencies and consequent discrimination in reception against the higher audio frequencies by selec- Ative audio circuits which tend to restore the higher audio frequencies to their original relative 125 amount. If, however, this device is used very great distortion occurs unless the receiver is tuned exactly on the carrier Wave which it is desired -to receive. VAnother complication in achieving faithful reproduction is present when automatic volume control is employed. In this case the signal response to the operator remains relatively constant in volume over a considerable tuning interval and he has nomeans unless a visual meter is used other than` his judgment of tone quality to indicate to him the point of tuning for the best response as regards quality of reproduction; that is, with receivers constructed according to the most advanced present practice as regards faithfulness of reproduction and constancy of operation, it is necessary in tuning to pass through considerable intervals between the points of exact tuning Where the quality of reception is very bad and this is appreciated by the operator as a serious objection in the operation of thereceiver. He also objects tothe fact that between stations the sensitivity of such a receiver is maintained ata maximum. Consequently, static and noise are received at the maximum intensity at these points. The present invention obviates these disadvantages of the most advanced present day receivers by rendering the receiver inoperative by other means than through the ordinary selective networks, except in a narrow frequency band immediately adjacent to the point of exact tuning for the desired frequency, this band being preferably not more than one or two kilocycles wide. Throughout this band the normal characteristics of the ordinary selective circuits operate and the reception accordingly remains excellent throughout the band. At either side of it, however, there is a very sharp or entirely abrupt cutoff so that in the tuning interval where the quality of reception would ordinarily be poor the receiver is wholly inoperative. This method of operation can be secured in various ways. Five such ways of applying the principle of this invention are described as illustrative ways of carrying out the general method, one based on balanced mistuned additional selective circuits and the voltage response therein to the incoming signal, 'the second based on the voltage response thereto in an additional extremely selective circuit, not forming a portion of the regular selective circuits, and the third consisting of the use of a local oscillator tuned to the intermediate frequency developing beat frequencies in a control detector tube which beat frequencies when present actuate the cut-off device.

The fourth method uses the voltage response in a normal selective or resonant circuit to control the operation of a mechanism having relatively abrupt cut-off characteristics.

The fth method differs from the other four in affording a less abrupt independent control of the output of the receiver but uses the same general principle.

In the drawings,

Figure 1 is a block diagram of the second method;

Fig. 2 is a circuit diagram of a receiver using the same method;

Fig. 3 is a block diagram of a method based on the use of mistuned selective circuits;

Fig. 4 is a circuit diagram of a receiver using this. method of operation;

Fig. 5 is a plot of the current response against varying frequencies of the incoming signal in the detector controlled by the Very selective control circuit used in Figs. l and 2;

Fig. 6 is a plot of the voltage response in the main selector circuit used in Figs. 3 and 4 against the frequency of the incoming carrier, and of the voltage response of the mistuned selector circuits used to actuate the control mechanism against this frequency;

Fig. 7 is a portion of a receiving circuit in which the voltage response in a normal resonant circuit is used to control a special mechanism to obtain a sharper control of output with variation of the resonant frequency than the voltage response is itself capable of producing;

Fig. 8 and Fig. 9 are plots. showing the voltage response in two portions of the circuit shown in Fig. '7 as illustrating the operation of the device shown in this figure;

Fig. 10 is a block diagram similar to Figs. 1 and 3, of a method of control employing a local oscillator;

Fig. 11 is a circuit diagram of the receiver shown more diagrammatically in Fig. 10; and

Fig. 12 is a portion of a circuit diagram showing a less. abrupt independent method of control than is illustrated in the four preceding methods.

In'Fig. 1 Ithere is given a block diagram of apparatus for carrying out this method in which the change in voltage in resonant circuits when change in frequency in the incoming signal occurs is directly employed to obtain the result desired. In this gure and in Figs. 3 and 10 solid vmatic volume control system 10.

lines denote signal currents and dotted lines denote control currents. In this figure, 49 is an antenna system; 5i) a radio frequency amplifier; 5I a heterodyne oscillator; 52 a first detector; 53 an intermediate frequency amplier; 54 is an automatic volume control system receiving signals from the last stage of an intermediate frequency amplifier 53 and in turn controlling one or more tubes in that amplifier and in the radio frequency amplifier 50. Signal voltage in this Way is maintained at relatively constant voltage at the last stage of the intermediate frequency amplifier 53 from which point the second detector 55 is controlled. The second detector 55 furnishes. signals to the audio frequency amplier 56. The output of the audio frequency amplifier 56 passes to the output amplifier 5l through the cut-off device 58 and the output amplifier 5l supplies loud speaker 59. Signals from the automatic volume control system 54 pass to the sharp selective circuit 60 and the voltage in this circuit controls the operation of the control tube 6| which controls the cut-off device 58.

Referring now to Fig. 2, which shows the circuit diagram corresponding to the block diagram in Fig. l, to the right of the lines A-A in Fig. 1, there is shown the last intermediate frequency stage of amplification 62 consisting of resonant circuit 63, screen grid tube '64 and resonant circuit 64a. The intermediate frequency stage 62 impresses a signal on the resonant circuit 64b, the potential of which is. applied to the grid of the second detector 65. The grid of this tube is negatively biased by the resistance 264 shunted by the condenser 205 in the lead from the negative supply to the cathode of this tube. This negative bias may be increased by the automatic Volume control system later to be described. The varying plate current in the second detector tube 65 passing through the resistance 205 induces variations in the potential at the point between the plate and the resistance 205 corresponding with the variations in the plate current itself. These variations are transmitted by way of the condenser 205l to the end of the resistance of the normal volume control 6l, the variable contact of which impresses a proportional varying potential on the grid of the audio tube 66. The grid of this tube is negatively biased by the resistance 258 shunted by the condenser 259 in the lead from the negative supply to the cathode of this tube.

The varying plate current in the tube 66 so obtained impresses through the transformer 20'( a varying potential on the grids of the push-pull amplifier tubes 53, the plate currents of which pass through the primary of the speaker transformer 69, the secondary of which operates the loud speaker 208. There is supplied the auto- This consists of the screen grid tube 'H the grid of which is biased approximately to cutoff by the battery 'l2 through the resistance 263. Its screening grid is biased by the battery 209, the battery 2H) energizing its plate circuit through the resistance 13 and the tuned circuit 15. The grid potential of the tube 'H is, however, also affected by the potential in the resonant circuit 64b through the lead 222, the condenser 223 being interposed in the lead 222, and through the resistance 13 and condenser 260. Increase of potential in the resonant circuit 04h causes changes in the bias of the control grid'in theA tube 1| and increases in plate current in this tube. The plate current of this tube passes through the lead 224 and through the automatic volume control plate load resistance 13. The potential across the resistance 13 is increased with increase of plate current in the tube 1 I, and this. increase in potential serves to bias more negatively the control grid of the amplier tube 54 acting at the intermediate frequency and also the control grid in one or more tubes of the radio frequency amplifier, not shown in this figure. This change in control grid bias decreases the amount of amplification, this mechanism tending to preserve a relatively constant voltage in the resonant circuit E41 over very wide ranges of intensity of incoming signals. The plate current of the automatic volume control tube 1I also passes through the coil 14 constituting part of the very selective resonant circuit 15 which is coupled with the highly selective resonant circuit 16. There. is provided the control tube 11, the grid of which is normally biased approximately to cutoff or beyond by the battery 18, whose plate circuit is energized bythe battery 2l I. The potential in the resonant circuit 16 is, however, also applied to the grid of this. tube. The plate circuit of this tube serves to energize the relay 19. This relay operates the Contact points 80 which normally,- that is, when no current is flowing in the plate circuit of the control tube 11-are in contact, and when in such contact, serve to short circuit the primary of the audio transformer 201. Under these conditions the plate current of the audio tube 86 does not pass through the primary of the transformer 201 and the system is inoperative beyond this point. 1

As the frequency of the signal impressed upon the last stage of the intermediate frequency network approaches the resonance frequency of the tuned circuits I5 and 16, the voltage in 16 rises, Causing flow of current in the plate circuit of the control tube 11. As circuits 15 and 16 are very selective this: rise is very sharp as the resonance frequency is approached and might be represented by the curve in Fig. 5, abscissa representing the departure from the resonance frequency and the ordinates current response. When the current increases above the value 7c, say, in this figure, the armature of the relay 19 is attracted and separate the points 80 and the transformer 201 thereupon becomes operative. Relays have commonly the characteristic of asymmetric operation in such manner that the rising current necessary tc operate them is considerably greater than the falling current at which operation in the reverse direction occurs. There is, accordingly, provided the shunt resistance 8|. Passage of current through it is controlled by the contact points 82. On operation of the relay the points 82 are closed and the current through the relay is thereby reduced the necessary amount to insure that the amount of plate current necessary to operate the relay in one direction is about the same as the current below which it is necessary to go to operate the relay in the other direction.

.ln the preceding description I have described a method and apparatus for obtaining a control of the operation of a radio receiver, added to the ordinary selective networks and having sharper tuning characteristics than such networks can be made to possess without interfering with the quality of reception, the control being based on a method in which the change of voltage in independent resonant circuits, when change in the incoming frequency occurs, is directly used tocbtain the result desired. It is possible to use numerous other ways of obtaining this result utilizing again the samegeneral principle of adding an independent mechanism for selection on the ordinary selective networks.

In Figs. 3, 4 and 6, there is shown a method of securing a sharp cutoff imposed on the ordinary methods of selection of energy carrier by use of selective resonant circuits. Referring first to Fig. 3, which is a block diagram figuring the various circuit elements and their relation to one another, the antenna I transmits the incoming signal to the radio frequency amplifier 2 where the resulting radio frequency signal is amplified. The local oscillatorl 3 produces al local oscillating current, the two producing, by means of the rst detector 4, the intermediate frequency signal which is amplified in the intermediate frequency amplifier 5.

The automatic volume control system 6, controlled in the usual way by the signal voltage resulting from operation of the intermediate frequency amplifier 5, controls one or more tubes in the radio frequency and intermediate frequency systems by varying the grid bias in the usual way to obtain constant output of the intermediate frequency amplifier 5. The output of this amplifier is now impressed on three selector circuits 1, 8 and 9, 8 being tuned to the intermediate frequency, 1 being tuned toa slightly higher frequency and 9- to a slightly lower one, the difference in resonance frequencies from the base frequencies, plus and minus, being approximately equal in the two cases. Figure 6 shows the voltage response of these three selector circuits with change of frequency of the incoming signal, frequency being plotted as the abscissae, and the voltage response in the three circuits being plotted as ordinates forming the curves 1a, 8a and 9a. It will be seen that the voltage responses in selectors 1 and 9 are equal at but one frequency, this frequency being the point of exact resonance forselector circuit 8. If, now, the voltage responses in 1 and 9 are opposed their algebraic sum is zero only at this frequency. A phasev correcting system may be used so that these voltages do add exactly to zero. vSuch systems are well known and are omitted for simplicity. This combined opposed response is used to control the mistuning cutoff l Il which controls the cutoff device I I interposed between the audio amplifier 2I3 and the outut amplifier I2, in such manner that signals are allowed to pass tothe output amplifier I2 and to the loud speaker I3 only when the condition of zero output from the selectors 1 and 9 to the mistuning cutoff I is obtained.

Since, however, the condition of no incoming signal from the intermediate frequency amplifier will produce the condition of no input on the mistuning cutoff l0, from selectors 1 and 9, it is desirable to have a further control which renders the transmission of' signals possible only where a signal of the desired frequency ,is actually being received. The no signal cutoff I4 controlling cutoff device l5 is therefore provided, which is controlled from the selector circuit 8 in such manner as to render the transmission of signals (such as static, etc.) impossible unless current is flowing in the selector circuit 8. The cutoff device I5 is interposed between Vthe on resonance selector 8 and the second detector 2 I2.

A detailed circuit diagram of a receiving system capable of carrying out these functions is shown in Fig. 4. This diagram shows the circuit arrangements to the right of the line B-B in Fig. 3. Referring to this gure, i8 is the last stage of intermediate frequency amplification consisting of the screen grid tube |1 and oscillating circuit I8. The grid of the tube |1 is biased negatively with respect to the cathode by means of the resistance 26| interposed in the lead from the common -B return which is shunted by the condenser 262. The plate current from the tube |1 passes through the coils 1b, 8b and 9b, which are in coupled arrangement with the coils 1c, 8c and 9C of the resonant circuits 1, 8 and 9. The potential developed in the circuit 8 is impressed on the grid of the second detector tube 41 in the plate circuit of which is the resistance 48. The potential between the extremities of the resistance 48 is impressed through the condensers 99 and 9| on the resistance of the normal volume control 92, the variable contact thereof 93 being connected to the grid of the tube 94 of the first audio stage of amplification 95. 'I'he plate current of the audio tube 94 passes through the primary 96 of the push-pull transformer 91, the extremities of the secondary 98 thereof being connected to the grids of the push-pull tubes 3| and 32 of the second audio stage. The plates of these tubes are connected to the ends of the primary 99 of the speaker transformer |00, the secondary thereof, 9| actuating the loud speaker |02.

Returning now to the resonant circuits 1, 8 and 9, 1 is tuned to a frequency greater than the intermediate frequency, 8 is tuned to the frequency of the intermediate frequency and 9 is tuned to a frequency less than the intermediate frequency. The difference in the resonance frequencies of 1 and 8 is approximately the same as the difference between the resonance frequencies of 8 and 9. The circuits 1 and 9 are connected in opposed relationship and the difference of their voltage responses is impressed on the grid of the control tube I9 through the condenser 266. The grid of the control tube |9 is biased by the battery so that customarily no current flows through the plate circuit of this tube which is energized by the battery 2| and in which is included the plate load resistance 22 shunted by the condensers 2 5 and 226. One end of the plate load resistance 22 is connected through the biasing battery 23 with the cathode of the thyratron tube 24, the other end being connected to the grid of this tube, the battery 23 having such a potential that normally no plate current flows in this tube. The plate potential on the tube v24 is secured from the secondary of the transformer 25, the choke 26 and filter condenser 21 and the loading resistance 28 being provided, the resistance 28 being shunted by the condenser 2|1. Leads 29 and 30 are provided from the extremities of the resistance 28. Lead 29 passes to the middle of the secondary 98 of the push-pull transformer 91, the extremities of which are connected to the grids of the tubes 3| and 32. Lead 30 passes to the minus B supply of the push-pull tubes 3| and 82, from which through the resistance |03 connection is made to the cathodes of tubes 3| and 32. Under operating conditions no potential exists between the leads 29 and 30 and the grids of the output tubes 3| and 32 are biased only by the potential drop across the resistance |83. This is the case, as may be seen by reference to Fig. 6, when the intermediate frequency is at the proper value. Under these conditions the lvoltages developed in the resonant circuits 1c and 9c exactly cancel one another if proper phase correction is carried out and the biasing voltage of the battery 28 is such that no current flows in the plate circuit of the tube i9, and similarly the biasing voltage from the battery 23 is such that circuit of the thyratron tube 38 and consequently no current ows in the thyratron tube 24. If, now, the intermediate frequency approaches say the value f in Fig. 6, the potential in the oscillating circuit 1c has the value E1, whereas the voltage in the circuit 9c is E2 and their difference is no longer zero. Under these conditions the effective positive voltage on the grid of tube I9 is increased and current flows in its plate circuit. This in turn varies the bias of the grid in the thyratron tube 24 in a positive direction. These tubes have the characteristic that there is a certain critical potential which can be applied to the grid at which potential the change in plate current with change in the grid potential is extremely abrupt. A negative potential slightly greater than this potential insures that no current shall pass in the plate current. At a negative bias potential slightly less than this critical potential the grid loses its control and the impedance of the tube during one-half of the cycle becomes extremely small. Under these conditions the potential developed by the transformer during this half of the cycle is nearly wholly impressed on the plate load resistance 28 and this potential is manifested between the leads 29 and 30. Under these conditions the grids of the output tubes 3| and 32 are so heavily biased that they become inoperative and no operation of the loud speaker occurs.

As above noted, the foregoing control does not take care of the conditions where no signal on the desired frequency is being received. In order to prevent operation of the audio circuits under this condition there is supplied the control system 36 consisting of the control tube 31 and the thyratron tube 38 with their auxiliary apparatus. The grid of the control tube 31 is normally biased by the battery 2|6 approximately to cutoff. The plate of tube 31 is supplied by the battery 4| through the loading resistance 42. The potential developed in the circuit 8 is impressed through the condensers 39 and 49 on the grid of the tube 31, and when such a potential exists the bias is altered sufciently to allow current to flow in the plate circuit of this tube in which is the loading resistance 42. 'I'he resistance 42 is shunted by the condenser 2|9 and the cathode of tube 31 is coupled to the filament of tube 38 by the condenser 229. The grid of the thyratron tube 38 is similarly biased by the battery 43 through the resistance 42. The plate circuit of the thyratron tube 38 is energized by the secondary of the transformer 44, the primary of which is supplied with the line voltage, there being supplied the filter condenser 45, the filter choke |04, and the plate loading resistance 46 shunted by the condenser 22|. One extremity of the plate loading resistance 45 is connected to the cathode of the second detector tube 41 and the other to the plate through the plate loading resistance 48. When now there is no potential in the circuit 8, there is no flow of current in the plate circuit of the control tube 31 by reason of the grid bias. Similarly there is no flow of current in the plate there is no energizing potential on the plate of the\ second detector tube 41. This tube is consequently inoperative and no signal will be heard for that reason. In this way static bursts will not be heard in the loud speaker. When, however, a potential is impressed on the circuit 8 the biasing potential of the tube 31 is so modified as to permit plate current to flow in the control tube 31. This in turn modifies the biasing potential in the thyratron tube 38 below the critical point. The impedance of this tube accordingly drops nearly to zero on the positive one half of the cycle, and the potential developedin the transformer 44 is nearly wholly impressed on the loading resistance 4B andin turn on the plate of the second detector 41. This tube thereupon becomes operative and signals can be Atransmitted through-it.

The circuit is provided with Va usual type of automatic volume control system consisting of the tube 33 `on the grid of which is impressed the potential of the selective circuit 8 through the condensers 22,2 and 223. The. grid ofthe tube 33 is biased approximately to cutoff kby the 'battery 288 through the resistance 269. The plate circuit of the tube 33 energized byithe vbatter-y. 34 has in it the automatic volume control plate load resistance 35, and .the grid of. the intermediate frequency tube .I l is biased by the potential across theextremities of this resistance 35. The grid ofthe tube-SS-is biasedby the battery 36 so that under the condition of. low voltage on the circuiti) little .orne plate current flows in the plate circuit' of tube ,3.3. tential across the Aautomatic volume control plate loadresistance35 and the gridof thejtube` .I 'I is.

only -normallybiasedandworks at full sensitivity. As -voltage increases'in the circuit B the negative bias on the tube 33 is decreased, current flows in its plate .circuit 34.and potential is developed across its platelcad resistancev 35, which potential makes the bias of the grid of the tube I'I more negative and the amplification here decreases. This control can beand usually is extended to a tube in the radio frequency amplifier. 1

While it is. usually desirable that separate selective circuits be used of sharper tuningchar.- acteristics than'the normal selective circuits, it is not wholly necessary to .use them. We may, for example, have one part :of the circuit which has abroad tuning characteristic and another part of .the circuit which hasa sharper. tuning character. .This is particularly the. case if automatic volume control is employed.

. Referring to'Figs. '7, 3 and 9, there is shown a portion of a circuit infwhich this ,principle is utilized.- Theother portions of the circuit may conveniently .be similar-in character to that Vof Figs.. land 2. In Fig. 7, III) is ,the last stage of the intermediatev frequency amplifier from which are led the automatic volume control leads III and H2. Owing to the operation of the automatic volume control the tuning response to this circuit may have a shape somewhat similar to the curve-in Fig. 8. The resonant circuit II3, however, Which is coupled with this circuit, hasv a much sharper tuning characteristic which may be represented in Fig. 9. The potential of this circuit is impressed onthe grid of the seco-nd detector tube II4. It v is also, however, impressed through the blocking condensers 88 and IIE on the grid/of the thyra tron tube IIS, in addition ,to the biasing potential developed by the battery I-ll acting through the choke I I8. As before, this tube is energized by. the secondary of the transformer |05, the primary of which is energized bythe line voltage, there being provided the filter condenser IIS and the choke |29 together with the plate loading resistance |2| and by-pass condenser |22.- The potential across the resistance i2i is used to cause a plate potential in thesecond detector tube I I4l through the plate loading resistance |23, the potential across |23 leading to Ythe output through the condensers I24Vand `83. It is to be remembered that the thyratron tube; |I6 has a trigger or There is, therefore, little or no pocritical voltage necessary on the grid before plate current commences, and that Aafter it does commence the grid loses control. Accordingly, if the negative biasing potential developed by the battery II'I is above a certain amount, no current will ilowin the plate circuit of this tube and there will be noy plate supply tothe second detector tube I I4. When, however, the peak voltage in the resonant circuit II3 rises above a certain trigger value, shown in Fig. 9, the thyratron tube IIS is suddenly invade operative. The second detector tube ||4 is energized and the receiver as a Whole becomes operative. Y A Y Itvwill be seen, by reference to Fig. 9, that if this trigger voltage isplaced at a proper value the'A frequency interval on either side of the base frequency within which the receiver is` operative is much narrower than the frequency interval within which maximum potential exists in the resonant circuit IIJ. The operation of the thyraron tubel ||6 may, of course, be .used to` vcontrol the operation of the receiver inv variousl other ways, for example, in providing a. proper bias. to the first audio stage or in numerous' other ways which will be apparent to those skilled in the art.

It will be seen that the above described circuits illustrate means for carrying out the method of operation described herein. Other methods are possible as abovenoted, for example, a local oscillator of variable frequency can be used in'which the variation in frequency is; made to go in step with the period of natural resonance of the selec.-

zerov at the point Where the selective networks are' in exact resonance with the frequency of the incoming signal. .The rectified current or a potential produced by its ow across a resistance may be usedin the same Way the opposed voltage response lof the mistuned selective circuits in Figs. 3 and 4 are used -to control 4the operation of the receiver proper.

The use of my method in this way but using a superheterodyne receiver for purposes of simplicity in description is guredin Figs. 10 and 11. vReferring to Fig. 10, |25 is the antenna or other collecting mechanism; |26 is the radio frequency amplierg' l|2.'I..is the -heterodyne oscillator, and |28 ,is the rst detector; |29 is the intermediate frequency amplie1..controlling .the automatic Volumefcontrol system YI,3Il which in turn controls one c-r Ymoreelemetlts of the radio frequency amplier'system |25 and/.the intermediate frequency amplifier system |29; `I3| is 'the no station cutoii-, and |3,2"ijs the cutoi .means actuated thereby; |33 is the second detector; |34 is the audio amplifier; |35 is the intermediate frequency limit oscil1ator;:j|36 is the control detector controlling the control' device I3]v Whichatuates the cutoff |38 which'isv interposed between the audio amplier k|34 andthe outputamplier |39, the output from |39 going to the loud speaker |40. .,Referringnow toA Fig. 11, which is a circuit diagram to the right of the line C-LC in Fig. 10, I4I is the last stage ofintermediate frequency Vamplification consisting .ofthe resonant circuit |42, the

resonant circuit |43 coupled therewith, the vacuum tube |44 on the grid of which is imposed the potential developed in the resonant circuit |43. Tube |44 is of the screen grid type, the screen grid being positively biased by the battery |45, the plate potential being supplied by battery |46 through the coils |41 and |48. The resonant circuit |49 is in coupled arrangement with the coil |41 and the potential developed therein is imposed on the grid of the second detector tube 50, the grid of which is biased negatively by the battery I5 The potential in the resonant circuit |49 is also imposed on the grid of the automatic volume control tube |52 through the condenser |53, in addition to the biasing potential developed by the battery |54 through" the resistance |55, the value of the potential developed by the battery |54 being such that ordinarily no current flows in the plate circuit of the tube |52. Potential for the plate circuit of the tube |52 is furnished by the battery |56 through the plate load resistance |51 which is by-passed by the condenser |58. The potential developed across the resistance |51 is impressed on the grid of the intermediate frequency amplifier tube |44 and also through the leads 83 andthe ground |59 on the grid of one or more of the radio frequency amplifier tubes, that is, the operation of this tube is such that an increase in potential in the resonant circuit |49 increases the bias on the grid of the tube |44 and on one or more of the radio frequency amplifier tubes to reduce the amplification at these points. The grid of tube |44 receives a positive bias on account of the resistance 269 shunted by the condenser` 210 connecting its cathode with the ground return. The potential developed in the resonant circuit |49 is also through the condenser |60 impressed on the grid of the tube |6|, the grid of which is biased by the battery 62 through the resistance 84, and the plate circuit of which is supplied by the battery |63 through the resistance |64, the battery |63 and the resistance |64 being shunted by the condenser |65. The potential developed on the resistance |64 is applied to the grid of the thyratron tube |68, the grid of which is also biased by the battery |61. The plate circuit of the thyratron tube |66 is energized bythe secondary of the transformer 85, the primary of which is energized by the line voltage', includes the choke |68, the filter condenser |69, and the plate loading resistance |10 which is shunted by the condenser |1|. The potential across the resistance |10 is applied to the plate of the second detector tube |50 through the plate loading resistance 12. The operation of this part of the system is as follows: Y

When no signal is being received, the grid of the tube |6| is so biased by the battery |62 that no current flows in the plate circuit. When a signal is received a potential exists in the resonant circuit |49, this bias is interfered with, and plate current flows. This produces a potential on the resistance |64 which decreases the biasing potential exerted by the battery |61 to a point Where the grid of the thyratron tube |66 becomes inoperative and current iiows in the plate circuit of this tube. This produces a potential on the resistance |10, which potential supplies current to the second detector tube |50 and renders it operative. The plate current in this tube flows through the resistance |12 and the variations of the potential on this resistance are applied through the condensers |13 and |14 to the resistance of the normal volume control |15, the contact point of this control being led to the grid of the first audio stage amplifier |16. The grid of this tube is biased by the battery 212 and its plate is supplied by the battery 213. The plate circuit of this tube passes through the primary of the push-pull transformer |11, the secondary potential of which is impressed on the grids of the push-pull tubes |18 and |19. The plate circuit of these tubes passes through the primary of the loud speaker transformer |80, the secondary thereof |8| energizing the coil |82 of the loud speaker |83.

There is provided the local oscillator 86 oscillating at the intermediate frequency consisting of the oscillating circuit |84, vacuum tube and plate battery |86, biasing battery |81, a feedback coil |88 coupled to the coil of |84 in the plate circuit of the tube |85, this circuit also including the coil |89. Coil |89, together with the coil |48 in the plate circuit of the intermediate frequency amplifier tube |44, are in coupled arrangement with the resonant circuit |90, the potential of which is impressed on the grid of the control detector tube |9|, this grid being biased by the battery |92. The plate circuit of this tube is supplied by the battery |93 and includes the resistance |94 shunted by the condenser 215. If there is a variation in frequency between the current in the coil |48 which is the incoming intermediate frequency on the coil |89 which is the base intermediate frequency, beat frequencies are imposed on the plate current of the tube |9| and the variations in potential thereby occurring are transmitted by means of the condenser |95 to the grid of the tube |96 which is also biased by the battery |91 through the resistance |98. The plate circuit of the tube |96 is energized by the battery |99, the current thereof passing through the coil of the relay 200. The tube |96 is ordinarily biased by the-battery |91 so: that no current ows in the plate circuit thereof. If, however, there are beat frequenciesl developed in the tube |9|, current flows in the plate circuit of |96 depending in amount on therfrequency of the beat frequencies developed. If it rises above a predetermined amount the relay 200 operates and in so doing'short-circuits the primary of the pushpull transformer |11 and shunts its coil through the resistance 202 by the points 203 as before. In this way the loud speaker |83 is thrown out of operation. As before noted, the apparatus just described controls the output of the receiver in such manner that it is only operative when the receiver is tuned to a resonance within a small frequency interval on either side of the signal frequency.

The preceding examples of the application of my invention have all contemplated a means of control in which the operation is sharper in character than that of the normal selective circuit. Under certain circumstances it is desirable to use a supplementary control n which the control is of less abrupt character. Such a control is shown in Fig. 12, which is a circuit diagram of a portion of a receiver using a control of this sort. The other portion of the circuit may be of any type as, for example, those shown in Fig. 2 or Fig. 4. In Fig. 12, 23| is a coil constituting part of the last stage of intermediate frequency amplification in coupled arrangement with the coil of the resonant circuit 232. The potential in this circuit is impressed on the grid of the second detector tube 233, the grid of this tube being biased by battery 234 and the plate being energized by the battery 235, the plate circuit including the resistance 236. The variations in potential at the point between this resistance and the plate of the tube 233 are impressed by means of the condenser 231 on one end of the resistance 238 of a normal volume control, the variable contact 239 of which is connected to the grid of the rst audio stage tube 248. This tube has its grid biased by the battery 24! and its plate circuit is energized bythe battery 242. Its plate-current passes through the primary of the push-pull transformer 243, the circuit from this point being like that iny the other examples shown.-

As before, the potential in the resonant circuit 232 is impressed via the condenser 244 to the grid of the automatic volume control tube 245, the grid of which is negatively biased by the battery 245 acting through the resistance 241. This tube, which is of the screen grid type, has its screen grid biased by the battery 248. Its plate circuit includes the resonant circuit 249 and the plate loading resistance 250 shunted by the condenser 254. The potential across the resistance-255 is applied as before as a biasing potential to control the operation'of one or more of the intermediate frequencies and radio frequency tubes, this control not being shown in these drawings.

In coupled relationship to the resonant circuit 249 is the resonant circuit 251, the potential of which is applied to the grid of the control tube '252 which is biased approximately `to cutoff by the battery 253. This tube which is of the screen grid type, has its screen biased by part of thepotential developed by the battery 254 which supplies the plate circuit. This circuit includes the resistance 255 shunted by the condenser 256 and the potential across the resistance 255is applied to the grid of the rst audio tube in opposition to the battery 24! which is initially of such Jpotential as to practically cut off the operation of this tube. When signal conditions exist in which the incoming frequency approaches that of the resonant frequency of the circuits249 and 251,l plate current flows in the control tubel2 52 andthe bias of the tube 240 is decreased Vsufliciently so that the tube becomes operative. In this way it will be seen a control is superimposed on the ordinary control offered by the selective circuit, to make the operation of the receiver more. selective and to remove the disadvantages in the way of noise between stations,.magnied static burst, etc., which ordinarily are met with in a receiver using automatic volume control. The control, however, differs from the controls previously described in being of more gradual character than is the case in the previous methods outlined. Y 1

All five of the examples previously given contemplate the use of a Superheterodyne circuit. It is, of course, possible to use identically the same principle of control in the case of a circuit employing tuned radio-frequency. Here, however, as the selective circuits are made continuously variable. it is necessary that the control mechanisms, whether the very selective circuit used in Fig. 1 or Fig. 2 or the mistuned selector circuits used in Fig. 3 and Fig. 4, or the local oscillator used in Fig. l and Fig. 1l, be themselves variable in resonant frequency and that by means of this variability they shall be made to preserve the same relationship to the corresponding variable tuned stages of radio-frequency that the, ,described control mechanisms bear to the xed intermediate frequency of the superheterodyne circuits described herein. As the problems here are wholly mechanical and the electrical considerations are Aprecisely .the same, this case of application has'not been specifically described, but it is to be noted that the invention may be extended to and comprises application to such uses. templated the use of automatic volume control, inasmuch as the method is peculiarly applicable to receivers using this device. It is, however, highly useful in receivers not employing automatic volume control and itsuse in such receivers also constitutes use of the invention.

The points of control also can be varied. from the points selected in these illustrative methods. Examples may include the operation from the detector in the case of tuned radiol frequency amplifiers or the second detector in the case of superheterodyne circuits, or as above shown from the automatic volume control tube, when this is used.

It will thus be seen thaty I have outlined a method of radio-receiver control which combines the advantages as regards selectivity of very sharply resonant circuits with the advantagesas regards quality, of reception selective mechanisms which are broader in selective character. also be seen that I have devised a method whereby certain disadvantages of modern receivers, particularly those provided with an automatic volume control are successfully met, in particular, the disadvantage of these receivers consisting of uncertainty inthe point vofexact coincidence of the receiver resonant frequency to the incoming signal and the increased noise between stations. Furthermore, in this way it is insured that the receiver must always operate at points in which the audio response is the most faithful reproduction of the original transmitted sound. It will also be seen that receivers operated ac.- cording to the methods outlined herein have an apparent selectivity which is very'high, which advantage increases the ease of operation thereof.

Furthermore, it is to be understood that kthe particular form of apparatus shown and described and the particular procedure set forth, areV presented for purposes of explanation and illustration and that various modiflcationsof said apparatus and procedure can be made without departing from my invention as defined in the appended claims.

What I claim is:

l. In a radio receiver, signal energy carrier resonant networks sufficiently broad in selective characteristics so as not to impair proper reception of a side band frequency of the energy carrier, and-a more selective resonant network, said more selective resonant network controlling by means of the voltageresponse therein caused by variations in the frequency of the incoming signal,

a control mechanism comprising means for ren-l dering possible the transmission vof thev signal whenever the voltage response in said' more selective network exceeds a desired amount and comprising means for rendering such transmission impossible whenever the voltage response in said more selective network is less than the desired amount. y

,72. In a -radio receiver, main signal selective and transmission circuits resonant to a signal carrier frequencyand a control tube having a grid and an ionized atmosphere, whereby saidI control tube has an abrupt .increase of plate current when the negative bias of the grid of saidV Similarly, the examples given have con- It Will Y control tube is slightly decreased below a certain critical value., means including a tuned network other than said main circuits kfor decreasing said .bias .below thecritical lvalue when the 15 frequency of the incoming signal departs a predetermined amount from the resonant frequency of the selector circuits, and means for causing such increase in plate current in the control tube to prevent transmission of the signal.

3. In a radio receiver, signal selective and transmitting networks, two mistuned selector circuits, a control tube the grid of which is biased to have a predetermined space current when less than a desired signal intensity is received and also controlled by the voltage difference of said two mistuned selector circuits, a control mechanism actuated by the plate current in the control tube, comprising means for causing the operation of said control mechanism to impair the transmission of the signal in said selective and transmitting networks.

4. In a radio receiver, main selective networks for the choice of signal energy carriers of a desired frequency, an automatic volume control mechanism, resonant circuits posterior to the point of actuation of said volume control and resonant to frequencies of about the carrier frequency of the signal, and an independent control mechanism, the point of actuation of said independent control mechanism being subsequent to said resonant circuits and posterior to the point of actuation of said automatic volume control mechanism, said independent mechanism being operatively associated with said resonant circuits,

` and means for causing said independent control mechanism to control the transmission of the signal.

5. In a radio receiver, main selective networks for the choice of signal energy carriers of a desired frequency, an automatic volume control mechanism, resonant circuits posterior to the point of actuation of said volume control and resonant to frequencies of about the carrier frequency of the signal, and an independent control mechanism, the point of actuation of said independent control mechanism being subsequent to said resonant circuits and posterior to the point of actuation of said automatic volume control mechanism, said independent mechanism being operatively associated with said resonant circuits, and means for causing said independent control mechanism to control the transmission of the signal, the point of control of said independent control mechanism being posterior to the point of actuation of said independent control mechanism.

6. In a radio receiver, resonant circuits for selecting, transmitting and amplifying a signal energy carrier frequency, together with mechanism for giving automatic lvolume, control of the output of the receiver, and a supplementary control mechanism responsive to the carrier frequency, such supplementary control mechanism being actuated from a point in the resonant circuits later as regards the direction of transmission of the signal to the point at which actuation of the automatic volume control mechanism is caused, means for causing such supplementary mechanism to be operated by any desired difference between the frequencyA of an incoming signal and the resonant frequency of said resonant circuits and means for causing such operation to impair transmission of the signal at some point in the receiver.

7. In a radio receiver, customary selective circuits and a second circuit of more sharply selective character, a control mechanism designed to render a portion of the customary circuits inoperative, means including said second circuit for controlling said control mechanism, said control mechanism including means to render said customary circuits inoperative except when the voltage response at some point in the second more selective circuit is above a predetermined fraction of the magnitude of the maximum voltage response in said more selective circuit.

8. In a radio receiver, customary tuned circuits having a given sharpness of selective characteristics, and a second selective circuit having a sharper tuning characteristic than the customary selective circuits, means for impressing the carrier frequency on said second selective circuit and means for causing the degree of response in the more selective circuits to control the transmission of signals in the customary selective circuit.

9. In a radio receiver, customary tuned circuits having a given sharpness of selective characteristics, and a second selective circuit having a sharper tuning characteristic than the customary selective circuits, means for impressing the carrier frequency on said second selective circuit and means for causing the degree of response in the more selective circuit to control the transmission of signals in the customary selective circuits, said means of control being provided with an abrupt operative character whereby change of operativeness of the receiver from full operative character to non-operative character occurs in a very small frequency interval on either side of the point of exact tuning for the given energy carrier.

10. In a radio receiver responding to an energy carrier of a given frequency, selective resonant networks, and a second more selective network in which a relatively large change of voltage response Voccurs when the resonance frequency of said second selective network is at a relatively small difference in frequency from that of the frequency of the energy carrier, means for varying such second network as to its resonant frequency substantially in step with the resonance frequency of the first selective networks used for reception, transmission and amplification of the incoming signal, and means for utilizing said large change of voltage response in said second selective network to control the transmission of the signal in the first selective circuits.

11. In a radio receiver responding to an energy carrier of a given frequency, selective resonant networks, sufficiently broad in selective character so as not to impair proper reception of the side band frequencies of the energy carrier, and two selector circuits, one having a resonance frequency slightly above that of the resonant frequency of the first selective networks used for reception, the other having a resonant frequency slightly below that of the first selective networks used for reception, the difference in resonance frequencies in each case being substantially the same, means for impressing the voltage response of the two mistuned selector circuits in opposed relationship on a cut-off mechanism, and means for operating said cut-off mechanism whereby one or more elements of the receiver are rendered inoperative whenever the sum of the opposed voltages of the two mistuned selector circuits departs substantially from zero.

12. In a radio receiver responding to an energy carrier of a given frequency, selective resonant networks, and two selector circuits, one having a resonance frequency slightly above that of the resonance frequency of the first selective networks used for reception, the other having a frequency-slightly below that of the first selective networks used for reception, the difference in on said cut-off mechanism and means for oper-H ating said cut-off mechanism whereby one or more elements of the receiver are rendered inoperative whenever the sum of the opposed voltages of the two mistuned selector circuits departs substantially from zero.

13. In a radio receiver responding to an energy carrier of a given frequency, a selective resonant network sufficiently broad in selective characteristics so as not to impair proper reception of the side band frequencies of the energy carrier, a local oscillator operating substantially at the resonance frequency of the selective or resonant network, means for regulating the transmission efficiency of said network in a sense opposite to received carrier amplitude variations, means for impressing the network signal output andthe output of the local oscillator on a detector tube, a control mechanism, means for utilizing the beat frequencies in the plate current of said detector tube to operate said control mechanism, and means for causing said operation to render a portion of the receiver inoperative.

14. In a radio receiver responding to an energy carrier of a given frequency, a local oscillator of variable frequency, means for impressingY the-output cf said local oscillator and said energy carrier on a detector tube whereby an energy carrier of an intermediate frequency is produced, selective resonant networks tuned to a fixed intermediate frequency, a second local oscillator oscillating at the fixed intermediate frequency, means for detecting the audio component of said intermediate frequency energy carrier and means for amplifying the same, means for impressing said intermediate frequency and the output of said second local oscillator .operating at the intermediate frequency on a second detecting mechanism whereby beat frequencies between said intermediate frequency and the output of said second oscillator may be detected, and means for causing such beat frequencies if above a desired frequency to impair the transmission of the signal energy in said radio receiver.

15. The method of operation of a radio receiver involving the selection of modulated radiant energy carriers of a given frequency, which comprises transforming such modulated energy carriers into electric current, filtering such current as to frequency components with such lack of sharpness as to secure adequate transmission of the side band frequencies of said modulated energy carrier, independently filtering said modulated energy carrier as to frequency components so as to obtain a second filtered electric current comprising the carrier frequency of the first current but a decreased proportion of the side band frequencies thereof, and causing the amplitude of the second or moreselectively filtered signal to control the transmission of the first or less selectively filtered signal.

16. In a radio receiver, main signal selective and transmission circuits, and a control tube having a grid and an ionized atmosphere, whereby said control tube has an abrupt increaseof plate current when the negative bias of the grid of said control tube is slightly decreased below a certain critical Value, means including a tuned input circuit otherthan said main circuits for decreasing said bias below the critical value and means for causing such increase in plate current in the control tubeto control transmission of the signal.

17. In a radio receiver, customary selective and transmitting networks, two mistuned selector circuits, a control tube the grid of which is biased to have a predetermined space current when less than a desired signal intensity is received and' range, and independently controlling the ampliiication of the modified signal by said amplified but unmodified signal after a selection of the .tter sufficient to render the independent control action sharper than.V said variable amplification action.v

19. In a radio receiving set, a radio frequency amplifying system, an audiofrequency amplifying system, means for automatically controlling the volume of the signal outputof the radio frequency amplier by adjustment of the sensitivity of the latter, means for automatically,controllingv the volume of thesignal output of the `audio frequency amplifier, in such a manner that its sensitivity is at a minimum when the sensitivity of the radio amplifier is substantially a maximum, said last mentioned means including a highly selective controlling circuit actuated by the output of the radio frequency amplifier. o

20. In a radio receiving set, a radio frequency amplifyingsystem, an audio frequency amplifying system, means for automatically controlling the volume of the signal output of the radio frequency amplifier by adjustment of the sensitivity of the latter, meansfor automatically controlling the volume of the signal output of the audio frequency amplifier in such a manner that its sensitivity is at a minimum when the sensitivity of ton said signal, further modifying the frequency of said signal to a frequency in the audioV v the radio amplifier is substantially a maximum f and no signals are received, said last control means including a highly selective resonant network adapted to pass onlysignals of a given frequency. v

21. In combination with an amplifier having an output circuit resonant to an operating superaudible frequency, a detector having an input circuit coupled to said circuit resonant to said frequency, an amplifier for the audible frequency output of the detector, said last amplifier being normally maintained inefficient to amplify, a control networlr havin-g an input circuit, sharply resonant to said super-audible frequencycou pled to said first output circuit, the output of said network beingjconnected to the audiblefrequency amplifier for rendering the latter efficient to amplify whenever energyof said super-audible frequency is impressed upon said super-audible frequency amplifier. y

22. In combination with an amplifier having circuit coupled to said circuit resonant to said frequency, an amplifier for the audible frequency output of the detector, said last amplifier being normally maintained inefficient to amplify, a control network having an input circuit, resonant to said super-audible frequency, loosely coupled to said first output circuit to secure high selectivity, the output of said network being connected to the audible frequency amplifier for rendering the latter efiicient to amplify whenever energy of said super-audible frequency is impressed upon said super-audible frequency amplifier.

23. In combination with an amplifier having an output circuit resonant to an operating superaudible frequency, a detector having an input circuit coupled to said circuit resonant to said frequency, an amplifier for the audible frequency output of the detector, said last amplifierY being normally maintained biased to cut-ofi' whereby it is ineicient to amplify, a control network having an input circuit, sharply reso-nant to said super-audible frequency, coupled to said first output circuit, the output of said network being connected to the audible frequency amplifier for rendering the latter efficient to amplify whenever energy of said super-.audible frequency is impressed upon said super-audible frequency amplifier.

24. In combination with an amplifier having an output circuit resonant to an operating superaudible frequency, a detector having an input circuit coupled to said circuit resonant to said frequency, an amplifier for the audible frequency output` of the detector, said last amplier being normally maintained ineicient to amplify, a control network having an input circuit, sharply resonant to said super-audible frequency, coupled to said rst output circuit, the output of said network being adjustably connected to the audible frequency amplifier for rendering the latter eicient to amplify whenever energy of said super-audible frequency is impresed upon said super-audible frequency amplifier.

25. In a radio receiver, the combination of an audio frequency amplifier, a network resonant to a desired operating frequency preceding the amplifier input, and coupled thereto, for providing an audio frequency signal to be amplifiecLineans for normally maintaining an input electrode of the amplifier biased to cut-off, and a control circuit connected between said electrode and a desired point in said network for sufficiently reducing the bias to render the amplifier conductive only when said signal is provided and said control circuit being substantially more selective than said resonant network.

26. In a radio receiver, the combination of an audio frequency amplifier, a network reso-nant to a desired operating frequency preceding the amplifier input, and coupled thereto, for providing an audio frequency signal to be amplified, means for normally maintaining an input electrode of the amplifier biased to cut-off, and a control circuit connected between said electrode and a desired point' in said network for sufficiently reducing the bias to render the amplifier conductive only when said signal is provided, said control circuit including a highly selective input resonant to the said frequency.

27. In a radio receiver, the combination of an audio frequency amplifier, a network resonant to a desired operating frequency preceding the amplifier input, and coupled thereto, for providing an audio frequency signal to be amplified, means for normally maintaining an input electrede of the amplifier biased to cut-off, and a control circuit of higher selectivity than said resonant network adjustably connected between said electrode and a desired point in said network for sufficiently reducing the bias to render the amplifier conductive only when said signal is provided.

28. In a radio receiver provided with at least a high frequency signal amplifier, a demodulator, a demodulated signal amplifier and a control arrangement, responsive to variations in signal intensity level, for adjusting the gain of said first amplifier in such a manner that the signal input level to the demodulator is substantially constant, a second control arrangement, responsive to variations in the gain of said first amplifier, for rendering the said second amplifier ineflicient when the gain of the first amplifier increases above a predetermined level, and said second control arrangement including a selective network resonant to anv operating signal frequency and the last named selective network having a higher degree of selectivity than said first control arrangement.

29. In a radio receiver provided with at least a high frequency signal amplifier, a demodulator, a demodulated signal amplifier and a control arrangement, responsive to variations in signal intensity level, for adjusting the gain of said first amplifier in such a manner that the signal input level to the demodulator is substantially constant, a second control arrangement, responsive to variations in the gain of said first amplifier and including a rectifier for developing a control bias potential, for rendering the said second amplifier ineiiicient when the gain of the first amplifier increases above a predetermined level, and said second control arrangement including a selective network resonant to an operating signal frequency and the last named selective network having a higher degree of selectivity than said first control arrangement.

30. In a radio receiver provided with at least a high frequency signal amplifier, a demodulator, a demodulated signal amplifier, and a control arrangement, responsive to variations in signal intensity level, for adjusting the gain of said first amplifier in such ,a manner that the signal input level to the demodulator is substantially constant, a second control arrangement, responsive to variations in the gain of said first amplifier and including a rectifier for developing a controlbias potential, for rendering the said demodulator inefiicient when the gain of the first amplifier increases above a predetermined level, and said second control arrangement includinga selective network resonant to an operating signal frequency and the last named selective network having a higher degree of selectivity than said first control arrangement.

31. In a superheterodyne radio receiver, tuning means including a frequency converting oscillator, manually controllable means for adjusting the tuning means to syntony with a desired incoming radio signal, means for silencing the receiver during the tuning operation until approximate syntony with the desired signal is attained, a local oscillator and means conjointly responsive to the intermediate frequency signal and to potentials derived from said Ilocal oscillator for abruptly rendering the silencing means inoperative when approximate syntony is attained and for maintaining the said silencing means inoperative during a further adjustment of the tuning means over a limited range.

KENNETH W. JARVIS. 

